Herpes simplex virus (HSV) is a major human pathogen that enters susceptible cells through a pH independent cascade of virus-cell interactions. While many studies focus on understanding the function of viral components, recent development allow investigation of the cellular components that contribute to HSV entry. The cellular component involved in initial attachment of virus is heparan sulfate (HS). The component(s) responsible for stable attachment, whether HS or a putative protein receptor, remains to be identified. The objective of this proposal is to isolate, identify and characterize the stable attachment receptor(s) used by HSV-1 during infectious entry. The research design exploits the unique opportunity provided by recent identification and characterization of cells that are poorly susceptible to HSV due to a defect in entry. The specific aims are (1) to transfer susceptibility from highly susceptible human cells to low or not susceptible cells to clone the gene(s) encoding the HSV stable attachment receptor(s), (2) to confirm and characterize a 110 kd protein from virus-cell blots as a biochemical approach to isolate and identify the protein(s) which serve as the receptor on human cells, and (3) to use reagents produced in Aims 1 and 2 to generate anti-receptor antibodies to characterize the receptor and its role in HSV entry and tropism. These different, but complementary, approaches should be synergistic to the overall objective. They are feasible because of availability of cells that lack a functional non- heparin-like receptor required in HSV entry. Identifying a stable attachment receptor for HSV-1 is important to long-term goals of a) understanding how viruses cross the cell membrane to initiate gene expression during natural infection, b) using herpesviruses as vectors, c) designing strategies for circumventing infection of HSV and other major human virus pathogens which cause morbidity and mortality, and d) determining molecular mechanisms for fusion and communication across biological membranes.